1. Field of the Invention
The present invention relates to pharmaceutical methods and products for use in the prevention or reduction of corneal subepithelial haze following laser vision correction surgery and other corneal injuries, especially photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).
2. Description of the Related Art
Laser refractive surgery is performed in increasing numbers on completely healthy eyes where adverse surgical effects are less acceptable than for diseased eye treatments. Complications attending laser refractive surgery, due to abnormal wound healing of the cornea, include central vision haze.
The cornea is responsible for two thirds of the refracting power of the eye, making it a candidate for surgical procedures aimed at refractive correction. The qualities of the wounds made by the ArF excimer laser suggested the concept of using such a laser to directly photoablate the cornea after removal of the epithelial layer. The effect is to reprofile the surface of the cornea, defining a new anterior radius of curvature, thereby altering the optical power of the cornea, a technique referred to as photorefractive keratectomy (PRK). The procedure is a reasonably safe, effective and predictable technique for correcting low to moderate myopia. The most frequently reported complications of PRK and any laser surgery, include glare, haloes, difficulty with night vision, decreased contrast sensitivity, transient increases in intraocular pressure, mild subepithelial haze and myopic regression [Chan T K, Ashraf M F, Azar D T. Photorefractive keratectomy (PRK) outcomes and complications. In: Azar D T, Steinert R F, Stark W J, eds. Excimer Laser Phototherapeutic Keratectomy. Baltimore, Md.: Williams & Wilkins; 1997:157–173; and Hadden O B, Ring C P, Morris A T, Elder M J. Visual, refractive, and subjective outcomes after photorefractive keratectomy for myopia of 6 to 10 diopters using the Nidek laser. J Cataract Refract Surg 1999;25:936–942.]
Laser refractive surgery is performed on the cornea of the eye using an excimer laser to correct myopia and other refractive errors. With photorefractive keratectomy (PRK), the whole corneal epithelium is removed and the excimer laser is applied to the Bowman layer and the anterior stroma. An ablation depth of approximately 10 microns corrects 1 Diopter of myopia. The resultant reshaping of the cornea alters its optical power. Alternatively, laser in situ keratomileusis (LASIK), uses a suction ring and a microkeratome to create a thin flap from the central corneal surface. The underlying stromal bed is treated with the excimer laser and the flap is repositioned. In the majority of PRK and LASIK cases, the refractive outcome is within ±0.5 Diopter of that intended. Re-epithelialization of the human cornea occurs usually within two to three days postoperatively. Post-laser surgery complications include excessive myopic regression and disturbances in corneal transparency (haze, cloudiness, scarring) due to irregularities in the wound healing process. Flap-related complications can also occur with LASIK. Efficacy outcomes in the long term are generally similar between the two procedures. Laser refractive surgery is elective and resembles cosmetic surgery since it is performed on completely healthy eyes. Complications in healthy eyes are even less acceptable than in diseased eyes. As the number of laser vision correction surgeries continues to increase exponentially, there is an even greater need to reduce complications such as subepithelial haze or cloudiness that can develop in some patients as a result of the procedure.
Corneal subepithelial haze or cloudiness following laser refractive surgery occurs as a result of the disrupted structure of the anterior stromal lamellae. Corneal haze is not apparent until a few weeks to a few months postoperatively. Its duration can be from weeks to months, with some occurrences lasting over a year. Its severity can be mild to strong. There is a wide variability in the reported prevalence of haze, but so far no effective remedy has been found to treat, reduce or prevent postoperative corneal haze.
There is a great need for a pharmacologically safe, effective drug that can prevent or reduce corneal haze after laser surgery and other corneal injuries. The present invention discloses such a drug and provides such a method.